Actions for Suppression of fine ash formation in pulverized coal flames. Quarterly technical progress report No. 2, January 1, 1993--March 31, 1993 [electronic resource].

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Suppression of fine ash formation in pulverized coal flames. Quarterly technical progress report No. 2, January 1, 1993--March 31, 1993 [electronic resource].

Published
Washington, D.C. : United States. Dept. of Energy, 1993.
Oak Ridge, Tenn. : Distributed by the Office of Scientific and Technical Information, U.S. Dept. of Energy.
Physical Description
9 pages : digital, PDF file
Additional Creators
University of Washington, United States. Department of Energy, and United States. Department of Energy. Office of Scientific and Technical Information
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Summary
The second major ash producing mechanism is the generation of a submicron aerosol through a vaporization/condensation mechanism. When the ash size distribution is plotted in terms of number density, the submicron mode generally peaks at about 0. 1 μm. When plotted in terms of mass, this mode is sometimes distinct from the residual ash mode, and sometimes merged into it. During diffusion-limited char combustion, the interior of the particle becomes hot and fuel-rich. The non-volatile oxides (e.g., Al₂O₃, SiO₂, MgO, CaO, Fe₂O₃) can be reduced to more volatile suboxides and elements, and partially vaporized. These reoxidize while passing through the boundary layer surrounding the char particle, thus becoming so highly supersaturated that rapid homogeneous nucleation occurs. This high nuclei concentration in the boundary layer promotes more extensive coagulation than would occur if the nuclei were uniformly distributed across the flow field. The vaporization can be accelerated by the overshoot of the char temperature beyond the local gas temperature. Although these particles represent a relatively small fraction of the mass, they can present a large fraction of the surface area. Thus, they are a preferred site for the condensation of the more volatile oxides later in the furnace. This leads to a layering effect in which the refractory oxides are concentrated at the particle core and the more volatile oxides resideat the surface. This also explains the enrichment of the aerosol by volatile oxides that has been noted in samples from practical furnaces. These volatile metal oxides include the majority of the toxic metal contaminants, e.g., mercury, arsenic, selenium and nickel. Risk assessment studies suggest that toxic metal emissions represent a significant portion of the health risk associated with combustion systems.
Report Numbers
E 1.99:doe/pc/92548--t1
doe/pc/92548--t1
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Other Subject(s)
Note
Published through SciTech Connect.
04/29/1993.
"doe/pc/92548--t1"
"DE93015053"
Hoffman, D.A.; Butcher, E.K.; Kramlich, J.C.
Type of Report and Period Covered Note
Quarterly; 01/01/1993 - 03/31/1993
Funding Information
FG22-92PC92548
View MARC record | catkey: 13839198